The present invention relates to utility knife blades, and more particularly, to composite utility knife blades wherein the outer cutting edge of the blade is made of a highly wear-resistant alloy, and a backing portion of the blade is made of an alloy selected for toughness, such as spring steel. The present disclosure also relates to methods of making such composite utility knife blades.
Conventional utility knife blades are made of carbon steel and define a back edge, a cutting edge located on an opposite side of the blade relative to the back edge, and two side edges located on opposite sides of the blade relative to each other and extending between the back and cutting edges of the blade. A pair of notches are typically formed in the back edge of the blade for engaging a locator in a blade holder. Typically, the back, cutting and side edges of the blade define an approximately trapezoidal peripheral configuration.
Conventional utility knife blades are manufactured by providing a carbon steel strip, running the strip through a punch press to punch the notches at axially spaced locations on the strip, and stamping a brand name, logo or other identification thereon. Then, the strip is scored to form a plurality of axially spaced score lines, wherein each score line corresponds to a side edge of a respective blade and defines a preferred breaking line for later snapping the scored strip into a plurality of blades. The punched and scored strip is then wound again into a coil, and the coil is hardened and tempered. The hardening and tempering operations may be performed in a xe2x80x9cpit-typexe2x80x9d vacuum furnace wherein the coils are repeatedly heated and cooled therein. Alternatively, the hardening and tempering operations may be performed xe2x80x9cin-linexe2x80x9d, wherein the strip is unwound from the coil and successively driven through a series of furnaces and quenching stations to harden and temper the strip. The carbon steel strip is typically heat treated to a surface hardness of about 58 Rockwell xe2x80x9ccxe2x80x9d (xe2x80x9cRcxe2x80x9d), and thus defines a relatively hard and brittle structure.
The heat treated strip is then ground, honed and stropped in a conventional manner to form the facets defining a straight cutting edge along one side of the strip. Then, the strip is snapped at each score line to, in turn, break the strip along the score lines and thereby form from the strip a plurality of trapezoidal shaped utility knife blades. Because the entire strip is relatively hard and brittle (about 58 Rc), the strip readily breaks at each score line to thereby form clean edges at the side of each blade.
One of the drawbacks associated with such conventional utility knife blades is that each blade is formed of a single material, typically carbon steel, that is heat treated to a relatively hard and brittle state, typically about 58 Rc. Thus, although such blades define a relatively hard, wear-resistant cutting edge, the entire blade is also relatively brittle, and therefore is subject to premature breaking or cracking in use. In addition, the cutting edges of such conventional blades are frequently not as wear resistant as might otherwise be desired. However, because the entire blade is made of the same material, any increase in hardness, and thus wear resistance of the cutting edge, would render the blade too brittle for practical use. As a result, such conventional utility knife blades are incapable of achieving both the desired wear resistance at the cutting edge, and overall toughness to prevent cracking or premature breakage during use. Another drawback of such convention utility knife blades is that the carbon steel typically used to make such blades corrodes relatively easily, thus requiring premature disposal of the blades and/or costly coatings to prevent such premature corrosion.
Certain prior art patents teach composite utility knife blades defining sandwiched, laminated, or coated constructions. For example, U.S. Pat. No. 4,896,424 to Walker shows a utility knife having a composite cutting blade formed by a body section 16 made of titanium, and a cutting edge section 18 made of high carbon stainless steel and connected to the body section by a dovetail joint 25.
U.S. Pat. Nos. 3,279,283, 2,093,874, 3,681,846, and 6,105,261 relate generally to laminated knives or razor blades having cutting edges formed by a core layer made of a high carbon steel or other relatively hard material, and one or more outer layers made of relatively softer materials. Similarly, U.S. Pat. Nos. 3,911,579, 5,142,785, and 5,940,975 relate to knives or razor blades formed by applying a relatively hard carbon coating (or diamond like coating (xe2x80x9cDLCxe2x80x9d)) to a steel substrate. In addition, U.S. Pat. Nos. 5,317,938 and 5,842,387 relate to knives or razor blades made by etching a silicon substrate.
One of the drawbacks associated with these laminated, sandwiched and/or coated constructions, is that they are relatively expensive to manufacture, and therefore have not achieved widespread commercial use or acceptance in the utility knife blade field.
In stark contrast to the utility knife blade field, bi-metal band saw blades have been used in the saw industry for many years. For example, U.S. Reissue Pat. No. 26,676 shows a method of making bi-metal band saw blades wherein a steel backing strip and high speed steel wire are pre-treated by grinding and degreasing, and the wire is welded to the backing strip by electron beam welding. Then, the composite band stock is straightened and annealed. The sides of the annealed stock are then dressed, and the band saw blade teeth are formed in the high speed steel edge of the composite stock by milling. Then, the teeth are set and the resulting saw blade is heat treated. There are numerous methods known in the prior art for heat treating such band saw blades. For example, International Published Patent Application No. WO 98/38346 shows an apparatus and method for in-line hardening and tempering composite band saw blades wherein the blades are passed around rollers and driven repeatedly through the same tempering furnace and quenching zones. The heat treated composite band saw blades are then cleaned and packaged.
Although such bi-metal band saw blades have achieved widespread commercial use and acceptance over the past 30 years in the band saw blade industry, there is not believed to be any teaching or use in the prior art to manufacture utility knife blades defining a bi-metal or other composite construction as with bi-metal band saw blades. In addition, there are numerous obstacles preventing the application of such band saw blade technology to the manufacture of utility knife blades. For example, as described above, conventional utility knife blades are manufactured by forming score lines on the carbon steel strip, and then snapping the strip along the score lines to break the strip into the trapezoidal-shaped blades. However, the relatively tough, spring-like backing used, for example, to manufacture bi-metal band saw blades, cannot be scored and snapped. Rather, such relatively tough materials require different processes to form the utility knife blades from a heat treated, composite strip. In addition, the heat treating applied to conventional utility knife blades could not be used to heat treat bi-metal or other composite utility knife blades.
Accordingly, it is an object of the present disclosure to overcome one or more of the above-described drawbacks and disadvantages of prior art utility knife blades and/or methods of making such blades, and to provide a bi-metal or other composite utility knife blade defining a relatively hard; wear-resistant cutting edge, and a relatively tough, spring-like backing, and a method of making such utility knife blades.
The present invention is directed to a composite utility knife blade comprising a back edge, a cutting edge located on an opposite side of the blade relative to the back edge, and two side edges located on opposite sides of the blade relative to each other and extending between the back and cutting edges of the blade. Preferably, the back, cutting and side edges of the blade define an approximately trapezoidal peripheral configuration. The composite utility knife blade of the present invention further defines first and second metal portions, wherein the first metal portion extends between the back edge and the second metal portion, and further extends from approximately one side edge to the other side edge of the blade. The first metal portion is formed of an alloy steel heat treated to a hardness within the range of approximately 38 Rc to approximately 52 Rc. The second metal portion defines the cutting edge, and extends from approximately one side edge to the other side edge, and is formed of a high speed or tool steel heat treated to a hardness within the range of approximately 60 Rc to approximately 75 Rc. A weld region of the blade joins the first and second metal portions and extends from approximately one side edge to the other side edge of the blade.
In accordance with an alternative embodiment of the present invention, prior to hardening, the high speed or tool steel edge of the composite strip is cut, such as by punching, at the interface of each shear line and the second metal portion, to thereby separate the high speed steel cutting edges of adjacent composite utility knife blades formed from the composite strip. Then, during the die-cutting step, only the first metal portion of the hardened composite strip is die cut along the axially spaced shear lines to thereby form the plurality of utility knife blades from the composite strip. One advantage of the utility knife blades of the present invention is that they provide an extremely hard, wear-resistant cutting edge, and an extremely tough, spring-like backing, particularly in comparison to the conventional utility knife blades as described above. Thus, the utility knife blades of the present invention provide significantly improved blade life, and cutting performance throughout the blade life, in comparison to conventional utility knife blades. In addition, the utility knife blades, and method of making such blades, is relatively cost effective, particularly in comparison to the composite utility knife blades defining sandwiched, laminated and/or coated constructions, as also described above. As a result, the utility knife blades of the present invention provide a combination of wear resistance, toughness, cutting performance, and cost effectiveness heretofore believed to be commercially unavailable in utility knife blades.
Other objects and advantages of the present invention will become readily apparent in view of the following detailed description of preferred embodiments and accompanying drawings.